1. Field of the Invention
The present invention relates generally to intraocular lenses, and more specifically to intraocular lenses for providing accommodative vision to a human or animal subject.
2. Description of the Related Art
A young human eye is generally capable of focusing over a wide rage of distances in a process known as accommodation. Optically, the range of positions is largely accomplished by changing the power of the natural lens. The natural lens is deformed by the eye to modify the power. A human eye can suffer diseases that impair a patient's vision. For instance, a cataract may increase the opacity of the lens, which impairs vision and may ultimately result in blindness. To restore the patient's vision, the opaque lens may be surgically removed and replaced with an artificial intraocular lens, or IOL. An IOL may also be implanted to treat presbyopia or for other elective ocular surgical procedures.
Monofocal IOLs have a single focal length, or equivalently, a single power. Single focal length IOLs cannot accommodate. Rather, they provide clear vision only over a limited range of distances. As a result, distant objects may appear in focus, while objects at a normal reading distance from the eye may appear blurred.
Vision over a broader range of distances can be obtained with multifocal lenses. Multifocal lenses provide different foci enabling the patient to see objects at multiple distances. Aspheric lenses can be configured to provide an extended depth of focus. Such lenses can improve vision, but there may also be an associated reduction in visual acuity or overall visual quality.
Another approach is to use an accommodating IOL, which can adjust its axial position and/or optical power within a range in response to action of ciliary muscles in the eye. As a result, the patient can focus on objects in a range of distances from the eye, rather than at one or more discrete distances. This ability to accommodate is of tremendous benefit for the patient, and more closely approximates the patient's natural vision. One of the challenges in accommodating IOL's is providing a sufficient range of accommodation with the limited amount of ciliary muscle force. In various implementations of the accommodating IOL's, these small forces are transferred through a haptic or support structure that absorbs a certain amount of the force. Haptic or support structures that maximize the shape changing and/or axial position shifting capability of the accommodating IOL are desired.